On state resistance is an important characteristic of a semiconductor device, such as a semiconductor device used in any of various switching applications. A low on state resistance in a planar device, such as a field effect transistor (FET) or a diode, is generally achieved by the use of multi-finger structures for pairs of electrodes. The multi-finger structures increase the total periphery of each electrode.
The development and implementation of devices with a semiconductor structure with extremely low sheet resistance, e.g., 200-300 Ohms/square, presents new considerations in the design of devices with low on state resistance. For example, when a low on state resistance device is manufactured using semiconductor layer(s) with very low sheet resistance, the resistance of the semiconductor layer becomes comparable to that of the metal electrodes supplying the current to the device. In this case, the current density along the device finger becomes non-uniform. As a result, the device resistance does not decrease inversely proportionally to the finger width (e.g., the size of the dimension of the finger that is perpendicular to the direction of the current flow between the electrodes). Instead, as the finger width is increased, the device resistance per unit finger width first decreases, flattens over a range of widths, and then increases as the width is further increased.